In the start-up phase of the treatment of aqueous systems by activated carbon, it is typical to experience unacceptable increases in the pH of the effluent. These high levels of pH can last from 200 to 400 bed volumes, or several days of initial operation. The effect has also been experienced for granular activated carbons (GAC) already on-line and subjected to sudden changes in influent water chemistry (e.g. pH), or following their regeneration by chemical or thermal processes. When these spikes occur, the treated water does not meet the standards for distribution to the customer or discharge to the environment. This problem can lead to a significant loss in production, environmental problems, substantial fines, customer dissatisfaction, or expensive and tedious remedial actions.
The pH excursion phenomenon has been found to occur for various types of water treatment applications such as municipal surface water, wastewater, industrial process water, ground water, and point-of-use home water filter treatment applications. It has been found to exist using various types of granular activated carbons such as those produced from bituminous coal, subbituminous coal, wood, coconut, and peat feedstocks, or those which are acid-washed prior to use.
The presence of these pH excursions has been documented for many years, but has received greater attention recently due to increased monitoring. Little or nothing has been done to prevent or remedy the problem. The excursions have been largely tolerated because no solution was known to exist. Because of the growing concern for the environmental problems associated with these excursions as well as the economic losses, the greater knowledge in the use of activated carbon systems, and the stricter standards for the supply or discharge of water, it is an object of the invention to provide a method for eliminating them. Accordingly, it is an object of the present invention to provide an oxidized activated carbon that is useful in controlling pH excursions during the treatment of aqueous systems.